When a pressurized, sealed vessel, e.g. an aerosol vessel which contains special liquid with a low boiling point and vapor of the liquid, is overheated to an abnormal extent, the sealed vessel would explode by abnormally high inner pressure. In order to avoid such an accidental explosion, a conventional pressurized, sealed vessel (1) is equipped with a safety valve at a bottom plate (11) as shown by FIG. 1. This safety valve consists of a port (15) bored at the center of the bottom plated (11), a valve body (20) for closing the outside of the port (15) and a spring (21) for pulling the valve body (20) inward. When the sealed vessel (1) is abnormally overheated and the inner pressure increases to over a predetermined critical pressure, the valve body (20) is opened by the action of the highly-pressurized gas. Then the pressurized gas spouts from the part (15), and the inner pressure decreases to below the critical pressure.
However such a conventional safety valve has structural drawbacks; complexity of structure: inconvenient operation for assembling the bottom plate (11) to a cylinder of the vessel and a high cost of parts. These drawbacks are caused by the fact that the safety valve requires a plurality of parts to be assembled besides the valve body (20). In addition, the safety valve has also a problem from the standpoint of safety. If the valve body and a shaft for sliding through a hole are left unmoved for a long time, the sliding shaft would occasionally adhere to the edge of the hole or the valve body would sometimes adhere to the valve seat for some reasons. Then the valve would not work even when it is overheated.